The advancement of high speed printing equipment, such as dot matrix and ink jet printers, has tremendously increased the speed in which a letter perfect document can be created. Due to the speed at which ink is applied to a document, a fresh and continuous reservoir of ink is required. Ink is usually supplied in disposable ink cartridges that are designed for easy installation on the printing equipment. Once a cartridge is empty, it can be easily removed and replaced with a new one.
Most prior art ink cartridges utilize negative pressure to draw the ink from the cartridge. The reservoir of ink is usually absorbed by a foam-like material that fills the cavity of the cartridge. Ink is expelled from the cartridge by using a partial vacuum that draws or sucks the ink from the foam-like material through an opening or nozzle located on the cartridge. A vent is required since air has to enter the cartridge to displace the ink as it is being drawn out. If an air opening is not present, the ink or other liquid cannot be properly drawn out of the cartridge.
One of the problems typically associated with ink cartridges, especially larger cartridges used in ink jet printers, is ink leaking through the air opening. Ink can possibly escape through the air opening if the cartridge is jostled or positioned such that some ink may accumulate in the air opening. Ink then can leak out along the outer wall of the cartridge or can splash onto surrounding areas. Ink can also be transferred to the hands or clothing of a person replacing or touching the cartridge. Certain types of ink can sometimes be very difficult to remove and can sometimes permanently stain articles of clothing.
This leakage problem has been of special concern during the shipment of the cartridges. During shipping, the cartridge can be inadvertently turned over so that the air vent is directly below the ink-filled cavity. Due to gravitational forces, some ink may trickle down from the absorbent foam material and can accumulate over the air vent. In this position, it is possible for an appreciable amount of ink to escape through the air vent. Also, the cartridge could possibly be agitated or jostled during shipment which could also cause some loss of ink through the air vent.
Some prior art ink cartridges avoid this leakage problem by using filter materials to prevent ink from leaking through the air vent. These filter materials, however, are often quite delicate and can be damaged during shipment. An ink cartridge having a defective filter may allow ink to leak to its outer surface and may have to be discarded because of this leakage. Or, a defective filter may cause leaking ink to block the vent so that the cartridge no longer works. Also, these filters can increase the cost of each ink cartridge.
Leakage can also occur if the ink cartridge is transported by airplane. Generally, the pressure inside the ink cartridge is slightly lower than the pressure outside the cartridge. When the cartridge is brought to a high altitude by an airplane, for example, the pressure outside the cartridge can become less than the pressure inside the cartridge. If this occurs and if the pressure differential is substantial, ink within the cartridge can be forced through the air vent where it again can cause a mess. Even if the cartridge can be cleaned for usage, there is a needless loss of ink and a possibility that the person cleaning the cartridge may become stained with ink.
While prior art ink cartridges are somewhat reliable, they have the above-mentioned shortcomings that diminish their usefulness. Therefore, there is a need to create an inexpensive, yet reliable, air vent for an ink cartridge that helps retain the ink within the cartridge, but yet allows an air passage for venting purposes.